Embodiments of the inventive subject matter generally relate to the field of virtual memory management, and, more particularly, automatic page promotion and demotion in multiple page size environments.
The IBM® POWER5+™ processor supports multiple page sizes (i.e., 4 KB, 64 KB, 16 MB, and 16 GB). The 64 KB pages can be divided into sixteen 4 KB pages (“demotion”) and sixteen 4 KB pages can be coalesced into one 64 KB page (“promotion”). Frequent requests for 4 KB pages can lead to a shortage of 64 KB pages and performance degradation for processes requiring 64K pages. When a threshold of remaining 64 KB pages is reached, a page size monitor daemon (PSMD) searches an available list of 4 KB pages that can be promoted. The 4 KB pages cannot be promoted unless the PSMD finds sixteen contiguous 4 KB pages, so promotion can be challenging.